Magmatism And Its Restriction On Mineralization Of Yueyawan Cu-Ni Sulfide Deposit In Eastern Tianshan

The East Tianshan tectonic metallogenic belt is the second largest copper-nickel sulfide deposit metallogenic belt in China.Most of the copper-nickel deposits are concentrated in the Kumtag sand ridge to Tulargen area.In recent years,with the discovery of Baixintan,Lubei and Yueyawan deposits,the copper-nickel deposits in this area have been discovered in west Kumtag ridge and north Dananhu-Tousuquan Island arc belt,and enlarged the scale of the copper-nickel metallogenic belt.Through systematic field geological survey and metallogenic study,the main understandings obtained in this paper are as follows:The Yueyawan basic complex rock mass is characterized by obvious lithofacies differentiation and multi-stage intrusion.The intrusion of magma is divided into three stages,the first stage is gabbro face,which constitutes the main body of the rock mass;the second stage is olivine gabbro face,which is the main metallogenic stage;and the third stage is pale-colored gabbro face.The mineralization and alteration of wall rock is obvious,malachite,limonite and serpentinization are important prospecting indicators.The main elements of the rock mass show that the total alkali content is low,m/f=0.53-1.97.The rock mass belongs to iron-based basic rock;trace elements show the characteristics of enrichment in LILEs such as Rb,Ba,Sr and depletion in HFSEs like Nb,Ta,Zr,Hf;rare earth elements show the characteristics of enrichment in LREEs and depletion in HREEs.The zircon U-Pb age shows that the diagenetic age of the pale-colored gabbro in the rock mass is 287.5±1.4Ma,and the tectonic setting was an extensional environment after the collision in early Permian,which is consistent with the metallogenic background of the copper-nickel sulfide deposit in the Huangshan metallogenic belt of the East Tianshan Mountains.The magma source area was the mantle,which is metasomated by the fluid derived from the early oceanic crust subduction material.The assimilation in the process of primitive magma evolution occurred in the magma source area,and there was almost no assimilation happened by the upper crust material during the ascending emplacement.Under the background of early Permian extension,the primitive magma formed by partial melting of mantle material of early subduction oceanic crust metasomatism occurred separation crystallization of olivine and pyroxene and assimilation and mixing of other melts in deep magma chambers,which saturated and melted S,and finally formed sulfide ore bodies.